1. Field of the Invention
The present invention relates to a wavelength conversion device.
2. Related Art
An optical frequency modulator utilizing the surface acoustic wave, an optical wavelength conversion device utilizing the polarization inversion of non-linear domain and so forth can be realized by periodically forming the domain inversion structure wherein the ferroelectric polarization is forcibly inverted. Especially, if the periodic domain inversion of non-linear optical materials becomes possible, a high-efficiency wavelength conversion device can be manufactured; and to convert a solid state laser beam, for example, by using the above wavelength conversion device will make it possible to build up a small and light short-wavelength light source, which can be applied to printing, optical information processing, optical application measurements and controls and so forth.
As the method of forming a periodic domain inversion structure in a ferroelectric non-linear optical material, the so-called electric field poling process has been generally known. This method forms a comb-shaped electrode on one principal plane of a ferroelectric single crystal substrate and a uniform electrode on the other principal plane, and applies a pulse voltage between these electrodes. This sort of method is disclosed in Japanese Patent Publication No. H8-220578A, Japanese Patent Publication No. 2005-70195A and Japanese Patent Publication No. 2005-70194A.
Generation of the second harmonics from a non-linear optical material such as lithium niobate single crystal needs to form the periodic domain inversion in the single crystal. And, after forming the periodic domain inversion structure in the ferroelectric single crystal substrate, the method forms a ridge channel optical waveguide onto the surface of the substrate by means of machine processing or laser processing. Here, to locate the periodic domain inversion structure inside the ridge optical waveguide will modulate fundamental wave incident onto the optical waveguide to higher harmonics.